Apparatus and method of re-adjusting convergence of a projection tv

ABSTRACT

A method and an apparatus of re-adjusting convergence of a projection TV are disclosed. The apparatus includes a display device on which an image is projected and at least one light-sensing element ( 101 ) being provided around the display device. The light-sensing element ( 101 ) is composed of first and second sub-sensors ( 101 a,  101 b) that generate separate output signals as a projected alignment pattern moves over the sub-sensors ( 101 a,  101 b). The apparatus further includes a microprocessor calculating a convergence re-adjustment vector by obtaining a location of the light-sensing element ( 101 ), from which a previous convergence correction was made. The location of the light-sensing element ( 101 ) is obtained by analyzing the output signals. By using the apparatus and method of present invention, the misconvergence of the projection TV can be corrected very quickly and precisely.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection TV, and more particularly,to an apparatus and a method of re-adjusting convergence of a projectionTV.

2. Discussion of the Related Art

In general, there are many ways to correct the convergence of aprojection TV having red/green/blue (R/G/B) projection tubes. FIG. 1illustrates an example of typical convergence correction devices for aprojection TV. The device shown in FIG. 1 includes R/G/B projectiontubes 18 r, 18 g, and 18 b; a screen 11; location detectors 12 placed oneach side of the screen 11; a pattern generator 15 generating analignment pattern; a signal switch/amplifier 16; and a convergencecompensator 14 controlling convergence yokes 17 r, 17 g, and 17 g inaccordance with signals outputted from the location detectors 12. Eachlocation detector 12 may include a phototransistor or a charged coupledevice (CCD) linear sensor for location detection.

A method of adjusting the convergence of a projection TV using thedevice shown in FIG. 1 will now be described in detail. First, thelocations of the location detectors 12 placed on each side of the screen11 are obtained using the signals outputted from the detectors 12. Next,a convergence error is calculated using the locations of the locationdetectors 12. Then the convergence is corrected based on the calculatedconvergence error value. However, the measured locations of the locationdetectors 12 are not precise enough due to many problems. For thatreason, the convergence correction performance based on the above methodis often unsatisfactory.

In order to solve at least the problems set above, a greater number ofphoto transistors or very expensive CCD linear sensors have been used,however, these create further problems of adding complexity to thesystem and increasing the production cost.

Alternatively, amorphous solar cells are often used for preciselymeasuring the locations of the detectors, but they require supplementaldevices such as an A/D converter and involve a complex algorithm forcalculating the convergence error value.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus and amethod for re-adjusting convergence of a projection TV thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide an apparatus and amethod of re-adjusting convergence of a projection TV using aconvergence re-adjusting system having a simple circuit structure,reducing the production cost.

Another object of the present invention is to provide an apparatus and amethod of re-adjusting convergence of a projection TV that is able toprovide an improved convergence correction performance.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anapparatus of automatically re-adjusting convergence of a projection TVaccording to the present invention includes a display device, on whichan image is projected; at least one light-sensing element being providedaround the display device, the light-sensing element being composed offist and second sub-sensors that generate separate output signals as aprojected alignment pattern moves over the sub-sensors; and amicroprocessor calculating a convergence re-adjustment vector byobtaining location of the light-sensing element, from which a previousconvergence correction was made, the location of light-sensing elementbeing obtained by analyzing the output signals.

Preferably, the apparatus further includes a convergence controllergenerating a convergence yoke current in accordance with there-adjustment vector; and a projection part converging the projectedimage in accordance with the yoke current.

Preferably, the apparatus further includes a comparative part providingan informative signal to the microprocessor, the informative signalindicating T_(horizontal) and T_(vertical) which represent each time atwhich the output signals cross each other as the projected alignmentmoves over the sub-sensors in a horizontal direction and a verticaldirection, respectively; and a memory storing the obtained location ofthe light-sensing element. The microprocessor obtains the location oflight-sensing element by taking horizontal and vertical positions of thealignment pattern at time=T_(horizontal) and T_(vertical), respectively.The re-adjustment vector starts from a present convergence location andends at a previous convergence location, at which a previous convergencevector starting from the location of the light-sensing element alsoends. The previous convergence vector is stored in the memory when theprevious convergence correction based on the previous convergence vectoris previously performed.

In another aspect of the present invention, a method of automaticallyre-adjusting convergence of a projection TV according to the presentinvention includes the steps of (a) projecting an alignment pattern andmoving the projected pattern over at least one light-sensing elementprovided around a display device, the light sensor including first andsecond sub-sensors; and (b) obtaining a location of the light-sensingelement by taking horizontal and vertical positions of the alignmentpattern at time=T_(horizontal) and T_(vertical), where =T_(horizontal)and T_(vertical) represent each time at which separate output signalsgenerated from the sub-sensors cross each other as the projected patternmoves over the sub-sensors in a horizontal direction and a verticaldirection, respectively.

The method further includes the steps of (c) calculating a previouslycorrected convergence location from the obtained location of thelight-sensing element, from which a previous convergence correction wasmade; (d) obtaining a convergence re-adjustment vector that begins froma present convergence location and ends at the previously correctedconvergence location; and (e) performing a convergence re-adjustment onan image projected on the display device in accordance withthere-adjustment vector.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 illustrates an existing convergence correction system for aprojection TV;

FIG, 2 illustrates an apparatus of automatically re-adjustingconvergence of a projection TV according to the present invention;

FIG. 3 illustrates a light sensor shown in FIG. 2 in detail and itscorresponding output signals as a projected alignment pattern moves;

FIG. 4 illustrate how a convergence re-adjustment vector is obtained fora projection TV in accordance with the present invention;

FIG. 5A illustrates how an alignment pattern moves over a light sensorin accordance with the present invention;

FIG. 5B illustrates how separate output signals are generated fromsub-sensors of a light-sensing element when an alignment pattern movesover the light-sensing element;

FIG. 6 illustrates a connection been a light-sensing element and acomparator in accordance with the present invention;

FIG. 7 illustrates installation positions of light sensors in aprojection TV; and

FIG. 8 is a flow chart illustrating a method of re-adjusting convergenceof a projection TV in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference number will be usedthrough the drawings to refer to the same or like parts.

One of the main principles of the present invention is to precisely andrapidly re-adjusting convergence of a projection TV by (1) initiallycalculating the locations of light-sensing elements by observingseparate output signals generated from two sub-sensors included in eachlight-sensing element and (2) calculating the misconvergence error usingthe light-sensing element locations.

FIG. 2 illustrates an automatic convergence re-adjusting apparatus for aprojection TV according to the present invention. As it can be seen fromthe figure, the apparatus includes a display device 100, a plurality oflight-sensing elements 101, a comparative part 102, a system controller103, a memory 104, a digital convergence controller 105, and aprojection part 106. Each light-sensing element 101 includes a firstsub-sensor 101 a and a second sub-sensor 101 b. The comparative part 102includes a comparator 110, an inverter 111, and a latch circuit 112. Thesystem controller 103 includes a local microprocessor 113 and a mainmicroprocessor 114.

There are a total of eight light-sensing elements 101 provided aroundthe display device 100: one on each corner and one on each side of thedisplay device 100. Alternatively, only four light-sensing elements 101may be provided: one on each side of the display device 100.

The number of the light-sensing elements 101 and their locations dependon the type of the convergence correction. For example, it is preferableto use eight light-sensing elements 101 for dynamic convergencecorrections as shown in FIG. 2 or to use four light-sensing elements 101on each side of the display device 100 for static convergencecorrections.

For static convergence corrections, it is preferable that the first andsecond sub-sensors 101 a and 101 b of each light-sensing element 101 arearranged side by side (up/down or left/right) with a predeterminedvertical or horizontal distance between them. On the other hand, it ispreferable that the sub-sensors 101 a and 101 b of each light-sensingelement 101 are located diagonally, as shown in FIG. 2, for dynamicconvergence corrections. Alternatively, the convergence re-adjustingapparatus of the present invention may include both types oflight-sensing elements: elements including side-by-side arrangedsub-sensors and diagonally arranged sub-sensors.

FIG. 3 illustrates one of the light-sensing elements 101 shown in FIG. 2in detail. The light-sensing element 101 shown in FIG. 3 includes afirst sub-sensor or 101 a and a second sub-sensor 101 b. The sub-sensorsare preferably amorphous solar cell type sensors, but other type ofsensors may also be used for the sub-sensors in the present invention.

Referring to FIG. 3, the first and second sub-sensors 101 a and 101 bare diagonally located at a predetermined horizontal and verticaldistance d from each other. The size of the light-sensing element 101,which is denoted as D, can be obtained by adding the sizes of bothsub-sensors and the distance d. For example, for a projection HDTVhaving a diagonal size of 60 inches and 1920 by 1080 pixels, thehorizontal and vertical sizes of each pixel of the TV screen areapproximately 0.69 mm. In this case, the distance d between thesub-sensors 101 a and 101 b is preferably about 0.69 mm, and it ispreferable that the size D is sufficiently larger than 0.69 mm (e.g.,D>6.9 mm).

The main reason of having two sub-sensors in each light-sensing element100 is to precisely measure the misconvergence of the projection TVusing an alignment pattern. In general, the convergence of a projectionTV is initially corrected in a factory. However, a misconvergence due toits environmental changes and surrounding devices occurs when a useruses the TV at home. Therefore, in order to correct the misconvergence,it is important to find a location from which the previous convergencecorrection was made. These will be explained in more detail withreferences to FIG. 4.

FIG. 4 illustrates how to correct the misconvergence of a projection TVin accordance with the present invention. In FIG. 4, P1 represents thelocation of the previous convergence corrected at a factory, and P2 isthe location of the present convergence moved from P1 due toenvironmental changes. P0 represents the location of a light-sensingelement. Therefore, an additional convergence re-adjustment is necessaryto move the location of the convergence from P2 to P1.

First of all, in order to find a vector c shown in FIG. 4, whichrepresents the direction and distance of the desired convergencere-adjustment, vectors a and b must be given. Vector a representsdistance and direction associated with the original convergencecorrection performed at a factory, and it starts from the location ofthe light-sensing element P0 and ends at P1. The vector a ispredetermined at a factory and stored in a memory included in theprojection TV, then the vector c can be easily found by obtaining thevector b using an alignment pattern in accordance with presentinvention. The vector b can be obtained easily by finding the locationof the light-sensor P0 since P2 is known.

As mentioned above, the convergence correction apparatus of the presentinvention initially finds the location of the light-sensing element 101P0 by moving a projected alignment pattern over the light-sensingelement in horizontal and vertical directions. Next, the location of thepresent convergence P1 is found since vector a (original convergencecorrection) is given. Finally, the vector c can be easily found usingthe locations of P1 and P2.

A method of obtaining the location of a light-sensing element inaccordance with the present invention will now be made with referencesto FIGS. 3, 5A, and 5B. In general, an alignment pattern for detectingthe location of a light-sensing element 101 includes red, green, andblue alignment patterns, and its rectangular are is reasonably largerthan the area of the light-sensing element 101. For the presentinvention, a 1 cm by 1 cm light-sensing element 101 and a 2 cm by 3 cmalignment pattern are used as shown in FIG. 5A.

First of all, as shown in FIG. 2, the local microprocessor 113 of thesystem controller 103 receives a command for a convergence re-adjustmentand sends the command to the digital convergence controller 105. Thenthe digital convergence controller 105 projects an alignment pattern onthe display device 100 through the RGB projection part 106 and moves theprojected alignment pattern over a light-sensing element 101 fordetecting its location.

As shown in FIG. 5A, the alignment pattern passes through a firstsub-sensor 101 a and a second sub-sensor 101 b of the light-sensingelement 101. FIG. 5B illustrates how first and second output signals,which are generated from the first and second sub-sensors 101 a and 101b respectively, vary in time as the alignment pattern passes over bothsub-sensors as shown in FIG. 5A. Referring to FIG. 5B, the first outputsignal varies in an interval between t1 and t2, in which the patternpasses over the first sub-sensor 101 a . Similarly, the second outputsignal varies in an interval between t3 and t4, in which the patternpasses over the second sub-sensor 101 b. Since the gain of the firstsub-sensor 101 a is preset to be a half of the gain of the secondsub-sensor 101 b, the peak of the first output signal is about 50% ofthe peak of the second output signal. The main reason of presettinggains of the first and second sub-sensors 101 a and 101 b in that manneris to easily detect the location of the pattern at time=Tx (the firstand second output signals cross each other at time=Tx). At time=Tx, thepattern passes over the center of the second sub-sensor 101 b . Thevertical location of the pattern at time=Tx will be used as the verticallocation of the light-sensing element 101 for correcting themisconvergence shown in FIG. 4.

If the area of the first sub-sensor 101 a is about 50% of the area ofthe second sub-sensor 101 b, presetting gains of the sub-sensors asdescribed above may not be necessary.

FIG. 6 illustrates a connection between a light-sensing element 101 andthe comparator 110. Referring to FIG. 6, in order to detect the locationof the pattern at time=Tx, the first and second sub-sensors 101 a and101 b are connected to the positive and negative terminals of thecomparator 110 respectively, and they send their output signals to thecomparator 110. The resistor having a resistance of R (100Ω<R<1KΩ) shownin FIG. 6 is an I(current)−V(voltage) conversion resistor of anamorphous solar cell. The present invention uses the resistor with R forI-V conversion, but an OP amplifier may be used instead.

A first resistor having a resistance of R/2 is connected between thepositive terminal of the comparator 110 and first sub-sensor 101 a forsetting the gain of the first sub-sensor 101 a to a half of the gain ofthe second sub-sensor 101 b . In addition, by providing a proper offsetvoltage ΔV between a ground and a second resistor having a resistance ofR/2, whose the other end is connected to the positive terminal, thesignal outputted from the comparator 110 can be always High even if bothsub-sensors do not receive any light and can be combined with anotheroutput signal in form of wired OR. Therefore, the present invention usesan OP amp having an open collector for the comparator 110, and a pull-upresistor is connected to an output of the OP amp (not illustrated).

FIG. 3 also illustrates the outputs of the comparator 110 shown in FIG.2 as an alignment pattern moves over one of the light-sensing elements101 in a horizontal or vertical direction. When the alignment patternarrives at about the center of the second sub-sensor 101 b , the outputsignals of both sub-sensors cross each other, and the output signal ofthe comparator 110 becomes low (L) from high (H).

Therefore, the horizontal and vertical locations of the light-sensingelement 101 can be obtained by observing the outputs of the comparator110. When the comparator 110 outputs an informative signal indicatingthe location of the light-sensing element 101, the inverter 111 reversesthe informative signal of the comparator 110. Then the latch circuit 112latches the reversed signal.

The convergence re-adjusting apparatus according to the presentinvention may include only one comparative part 102 connected to all thelight-sensing elements 101 as shown FIG. 2 for simplifying structure, orit may include eight separate comparative parts, each of which isconnected to each light-sensing element 101, for significantly reducingthe processing time.

FIG. 7 illustrates the installation positions of the light-sensingelements 101 in the projection TV. As it is shown, the light-sensingelements 101 are provided on the over-scan-area of the display device100. If, by any chance, there is not enough space available at the backof the display device 100, they can be provided at a distance (z) fromthe backside of the display device 100. However, the light intensity atthe distance z should be reasonably high for detecting light.

FIG. 8 is a flow chart illustrating a method of re-adjusting theconvergence of a projection TV in accordance with the present invention.First of all, the manufacturer of the projection TV performs an originalconvergence correction in a factory and stores an original convergencecorrection vector (direction and distance) associated with the originalconvergence correction in a memory included (S1). After anymisconvergence due to any environmental changes or surrounding devicesoccurs, the digital convergence controller 105 selects one of R/G/Balignment patterns and projects the selected alignment pattern on adisplay device 100 through the projection part 106 (S2).

Next, the system controller 103 selects one of a plurality oflight-sensing elements 101 provided around the display device 100 of theTV (S3). Then, it measures and stores the location of the selectedlight-sensing element (S4) by moving the projected alignment patternover the selected light-sensing element in horizontal and verticaldirections. The horizontal location L_(x) of the selected element is thehorizontal location of the alignment pattern at time=T_(x), where T_(x)is the time at which the output signals generated from the twosub-sensors of the selected light-sensing element cross each other whenthe alignment pattern moves in the horizontal direction. Similarly, thevertical location L_(y) of the sensor is the horizontal location of thealignment pattern at time=T_(y), where T_(y) is the time at which theoutput signals generated from the sub-sensors of the selectedlight-sensing element cross each other when the alignment pattern movesin the vertical direction. Then, the controller 105 stores the measuredlocation of the light-sensing element (L_(x) and L_(y)) in the memory.

Next, the system controller 103 check whether the locations of all thelight-sensing elements 101 corresponding to the selected alignmentpattern are stored in the memory (S5). If it is determined in the stepS5 that they are not, the controller 105 repeats the steps S3 and S4until the locations of all the sensors 101 are measured and stored inthe memory.

If the controller 105 determines that the locations of all the sensors101 corresponding to the selected alignment pattern are measured andstored in the memory in the step S5, it further checks whether thelocations of the light-sensing elements 101 corresponding to all of theR/G/B alignment patterns are measured and stored. If they are not, thecontroller 105 repeats the steps S2 to S5 until they are measured andstored.

On the other hand, if it is determined that the locations of all thesensors 101 corresponding to all the alignment patterns are measured andstored in the step S6, the local microprocessor 113 calculates are-adjustment vector (vector c), which represents the distance anddistance of a desired convergence re-adjustment (S7). It initiallyobtains the location of the original convergence (P1 shown in FIG. 4)for each light-sensing element 101 using the location of thelight-sensing element (P0) stored in the memory, and it calculates there-adjustment vector by P1 and P2, whore P2 represents a known locationof the present convergence.

Finally, the digital convergence controller 105 corrects themisconvergence of the projection TV in accordance with the re-adjustmentvector found in the step S7 (S8).

In the apparatus and method of re-adjusting convergence of a projectionTV, the location of each light-sensing element is measured using theoutput signals generated from the sub-sensors and alignment patterns.Therefor, the location of each light-sensing element can be preciselymeasure, and the sensitivity of each light-sensing element is greatlyimproved. In addition, the location of each light-sensing element ismeasured by directly observing the output signals of the sub-sensors,there is no need to use an expensive A/D converter. This means that themisconvergence of the TV can be corrected by a simple circuit structureaccording to the present invention.

Another advantage of the invention is that the location of eachlight-sensing element can be found by simply moving alignment patternsonly in horizontal and vertical directions.

Another advantage of the present invention is a high-speed process ofmeasuring the locations of the light-sensing elements because themeasurements are performed directly through a comparator.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the invention covers the modifications and variationsof this invention provided they come within the scope of the appendedclaims and their equivalents.

1. An apparatus of automatically re-adjusting convergence of aprojection TV, the apparatus comprising: a display device, on which animage is projected; at least one light-sensing element being providedaround said display device said light-sensing element being composed offirst and second sub-sensors that generate separate output signals as aprojected alignment pattern moves over said sub-sensors; and amicroprocessor calculating a convergence re-adjustment vector byobtaining a location of said light-sensing element, from which aprevious convergence correction was made, said location of light-sensingelement being obtained by analyzing said output signals.
 2. Theapparatus of claim 1, further comprising: a convergence controllergenerating a convergence yoke current in accordance with saidre-adjustment vector; and a projection part converging said projectedmade in accordance with said yoke current.
 3. The apparatus of claim 2,wherein said convergence controller provides a control signal to saidprojection pattern for moving said projected pattern over saidsub-sensors.
 4. The apparatus of claim 1, further comprising: acomparative part providing an informative signal to said microprocessor,said informative signal indicating T_(horizontal) and T_(vertical) whichrepresent each time at which said output signals cross each other assaid projected alignment moves over said sub-sensors in a horizontaldirection and a vertical direction, respectively; and a memory storingsaid obtained location of said light-sensing element.
 5. The apparatusof claim 4, wherein said comparative part includes a comparatorreceiving said output signals generated from said sub-sensors andgenerating said informative signal, an inverter inverting saidinformation signal, and a latch circuit latching said inverted signal.6. The apparatus of claim 4, wherein said microprocessor obtains saidlocation of light-sensing element by taking horizontal and verticalpositions of said alignment pattern at time=T_(horizontal) andT_(vertical), respectively.
 7. The apparatus of claim 6, wherein saidre-adjustment vector starts from a present convergence location and endsat a previous convergence location, at which a previous convergencevector starting from said location of said light-sensing element alsoends.
 8. The apparatus of claim 7, wherein said previous convergencevector is stored in said memory when said previous convergencecorrection based on said previous convergence vector is previouslyperformed.
 9. The apparatus of claim 4, wherein said first and secondsub-sensors are diagonally arranged within said light-sensing element orare arranged side by side within said light-sensing element.
 10. Theapparatus of claim 4, wherein a light-receiving area of said firstsub-sensor is about 50% of a light-receiving area of said secondsub-sensor.
 11. The apparatus of claim 4, wherein a gain of said firstsub-sensor is about 50% of a gain of said second sub-sensor.
 12. Anapparatus for automatically re-adjusting convergence of a projection TV,the apparatus comprising: a display device, on which an image isprojected; at least one light sensor being provided around said displaydevice, said light sensor being composed of first and second sub-sensorsgenerating separate output signals as a projected alignment patternmoves over said sub-sensors; a comparative part generating aninformative signal that indicates T_(horizontal and T) _(vertical),where T_(horizontal) and T_(vertical) represent each time at which saidseparate output signals cross each other as a said alignment patternmoves over said sub-sensors in a horizontal direction and a verticaldirection, respectively; a system controller calculating a convergencere-adjustment vector by obtaining a location of said light sensor fromwhich a previous convergence correction was made, said location of lightsenor being obtained by taking horizontal and vertical positions of saidalignment pattern at time=T_(horizontal) and T_(vertical), respectively;a convergence controller generating a control signal for moving saidalignment pattern and generating a convergence yoke current inaccordance with said re-adjustment vector; a projection part convergingsaid projected image in accordance with said current; and a memorystoring said obtained location of said light sensor.
 13. The apparatusof claim 12, wherein said light sensor is provided on a backside of saiddisplay device or at a predetermined distance behind said backside. 14.The apparatus of claim 12 wherein said light sensor is provided at eachcorner of said display device and an each of top, bottom, left, andright sides of said display device.
 15. The apparatus of claim 12,wherein said light sensor is provided on each of top, bottom, left, andright sides of said display device.
 16. The apparatus of claim 12,wherein said first and second sub-sensors are diagonally arranged withinsaid light sensor or are arranged side by side within said light sensor.17. The apparatus of claim 12, wherein a light-receiving area of saidfirst sub-sensor is about 50% of a light-receiving area of said secondsub-sensor.
 18. The apparatus of claim 12, wherein a gain of said firstsub-sensor is about 50% of a gain of said second sub-sensor.
 19. Theapparatus of claim 12, wherein said comparative part includes acomparator receiving said output signals generated from said sub-sensorsand generating said information signal, an inverter inverting saidinformation signal, and a latch circuit latching said inverted signal.20. A method of automatically correcting misconvergence of a projectionTV, the method comprising the steps of: projecting an alignment patternand moving said projected pattern over at least one light-sensingelement provided around a display device, said light sensor includingfirst and second sub-sensors; obtaining a location of said light-sensingelement by taking horizontal and vertical positions of said alignmentpattern at time=T_(horizontal) and T_(vertical), where =T_(horizontal)and T_(vertical) represent each time at which separate output signalsgenerated from said sub-sensors cross each other as said projectedpattern moves over said sub-sensors in a horizontal direction and avertical direction, respectively; calculating a previously correctedconvergence location from said obtained location of said light-sensingelement, from which a previous convergence correction was made;obtaining a convergence re-adjustment vector that begins from a presentconvergence location and ends at said previously corrected convergencelocation; and performing a convergence re-adjustment on an imageprojected on said display device in accordance with said re-adjustmentvector.
 21. The method of claim 20, further comprising the step ofstoring said obtained location of said light-sensing element in amemory.
 22. The method of claim 20, wherein said first and secondsub-sensor are diagonally arranged within said light-sensing element.23. The method of claim 20, wherein said first and second sub-sensorsare arranged side-by-side within said light-sensing element.
 24. Themethod of claim 20, wherein direction and distance associated with saidprevious convergence correction are previously stored in a memory. 25.The method of claim 20, wherein a light-receiving are of said firstsub-sensor is about 50% of a light-receiving area of said secondsub-sensor.
 26. The method of claim 20, wherein a gain of said firstsub-sensor is about 50% of a gain of said second-sensor.